The overall objective is to clarify the role in tumorigenesis of genetic factors on specific chromosomes, using, primarily, intraspecific hybrid cells in the mouse or other rodent cell lines and hybrids, developing additional chromosome banding methods and improving the accuracy of chromosome identification, with particular attention to heritable chromosome variants which can serve as markers. Hybrids will be produced between malignant and nonmalignant cells in which specific chromosomes, or the entire complement derived from one parent can be distinguished from the corresponding chromosomes derived from the other parent. Expression and suppression of facets of the malignant phenotype will be correlated with the presence or absence of specific chromosomes.